First of all I would like to thank everyone for their nice posts. I would also like to say sorry to classwife for missing the right category. There are so many to choose from!
I pulled this straight from nicotine article on Wikipedia:
Historically, nicotine has not been regarded as a carcinogen and the IARC has not evaluated nicotine in its standalone form and assigned it to an official carcinogen group. While no epidemiological evidence supports that nicotine alone acts as a carcinogen in the formation of human cancer, research over the last decade has identified nicotine's carcinogenic potential in animal models and cell culture.[65][66] Nicotine has been noted to directly cause cancer through a number of different mechanisms such as the activation of MAP Kinases.[67] Indirectly, nicotine increases cholinergic signalling (and adrenergic signalling in the case of colon cancer[68]), thereby impeding apoptosis (programmed cell death), promoting tumor growth, and activating growth factors and cellular mitogenic factors such as 5-LOX, and EGF. Nicotine also promotes cancer growth by stimulating angiogenesis and neovascularization.[69][70] In one study, nicotine administered to mice with tumors caused increases in tumor size (twofold increase), metastasis (nine-fold increase), and tumor recurrence (threefold increase).[71]
Though the teratogenic properties of nicotine may or may not yet have been adequately researched, women who use nicotine gum and patches during the early stages of pregnancy face an increased risk of having babies with birth defects, according to a study of around 77,000 pregnant women in Denmark. The study found that women who use nicotine-replacement therapy in the first 12 weeks of pregnancy have a 60% greater risk of having babies with birth defects, compared to women who are non-smokers.[citation needed]
Effective April 1, 1990, the Office of Environmental Health Hazard Assessment (OEHHA) of the California Environmental Protection Agency added nicotine to the list of chemicals known to the state to cause developmental toxicity, for the purposes of Proposition 65.
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This is where I got that line about Nicotine helping spread cancer once you already have the cells in your body. I cannot seem to find a lot of information on it but I know that all nicotine comes from tobacco and as such they must contain TSNAs (tobacco specific nitrosamine). I get that this is created only in the curing process but I also understand economics to know that they are going to acquire tobacco in the cheapest way possible to do their extractions and that is going to be by the traditional means.